CONTROL OF BROWN BAST IN ORGANIC RUBBER CULTIVATION

IN SOUTH INDIA

By Dr. Margarita Correa

PRESENTATION OF THE ORGANIC RUBBER TREES CULTIVATION

Located in South India, there is a organic rubber cultivation farm; with a population of around

225,000 trees within 7 to 33 years old in 1,400 acres of land. The main technologies followed in its

organic practices are:

1. Vermi technology

2. Probiotic Technology

3. Ayurveda on the plants

4. Homoeopathy on the plants

The main concern of this cultivation is the appearance in the last years of the disease named brown

bast.

OCCURANCE

The tapping panel dryness (Brown bast) is a serious disorder which reduces production. In

this the tapping panel dries and further production of latex is reduced. In most of the cases

the tree becomes unproductive for entire life. The dryness starts in any panel irrespective of

age. There are occasions where the dryness as has started from second year of tapping (i.e.

9th

year of age and A panel). The severity of the dryness varies from clone to clone and panel

to panel. It is more pronounced in renewed bark (C & D panels). Of late the visibility of

dryness is more in A & B panels also in high yielding clones.

RRII is been of the view that this is due to physiological disorder and by reducing the

intensity of tapping this can be reduced / avoided. Thus they recommended from D/2 system

(alternate daily) to D/3 system (3rd

daily) of tapping. Also when they released the high

yielding clones such as PB 235, PB 260 and RRII 105 a decade back they recommended 3rd

daily of exploitation in these clones from 1st year of tapping onwards. At that time other

clones were recommended to be on 2nd

daily system of exploitation. The incidence of brown

bast in those clones was also under threshold level at that time.

Of late the incidence of dryness is rampant. Eventhough all the clones are tapped once in

three days the incidence is found to be as high as 32% in certain clones. On an average the

present brown bast affected trees is 15.80% of the total population in this farm.

RRII recommendation for controlling the brown bast in a tree is of isolation principle. The

dried patch is isolated from rest of the tree by giving a deep cut to the wood around the dry

patch including some healthy bark. Bitumen or Rubberkote was advised to be painted on the

dry patch. The intention here is to isolate the dry patch from further spreading and apply an

ameliorant saving the tree from injury. But hardly this treatment contained the dryness. The

whole tree became unproductive in matter of years.

CONCERNS

The incidence is been growing of year on year leading to reduction in productive trees. The

theory of physiological disorder is questionable, as the incidence has started occurring in

virgin bark (A & B) also. RRII has not come out with concrete recommendations of

controlling the dryness.

BUILDING RESISTENCE

In the last UPASI conference pathologists from RRII submitted a paper that a viroid as

causative organism for the dryness. But there was no answer for question how it doesn’t

spread to next tree standing next to affected ones (as the infection can be easily spread by the

tapping knife while cutting the next tree). Another theory of the disease transmittance is

through seed and hence inherent to the plant.

Dr. Margarita Correa is of the view that the dryness is spreading through microorganisms.

These organisms were under check years back. Due to continuous cultivation practices

(inorganic fertilisers, chemicals and weedicides) the resistance of the individual trees to these

organisms has come down.

She has recommended usage of EM on the affected trees. Following is the method adopted.

EM extended – Preparation for Brown bast control

1 litre EM

1 Kg. organic jaggery

20 Litres Non-chlorinated raw water

All the above mixed in a plastic barrel, allowed to ferment in a dark room for 4 to 5 days; the

barrel should not disturbed and the pH of the solution should be < 3.8.

This EM activated is diluted to 1:50 by water at time of usage.

The affected trunks are to be covered tightly with a permeable cotton cloth (kada) from the

affected portion till the base. The cloth is tightly wound around the trunk so that entire cloth

is in contact with the bark. The affected trunk is sprayed with the above solution using a

knapsack sprayer before tying the cloth. After tying the cloth the trunk is sprayed again.

Then the cloth is sprayed every day with EM activated using knapsack in the morning. The

base of the affected tree is also sprayed once in 15 days at walking speed using knapsack

sprayer. All the spraying is done before 11 a.m. and the care is to be taken not to allow

sunlight to come in direct contact with EM activated containers

After a month the cloth has to be removed, washed thoroughly and put back. If the cloth is

impervious it has to be replaced. On the seeing the improvement the cloth can be removed

and the spraying can be extended to once in 15 days. Also the concentration can be 1: 500

(instead of 1:50). Once 75% recovery is noticed the spraying interval can be increased to

once in a month. Application can be throughout the year. Organic manuring pattern need not

be changed.

PROCESS CARRIED OUT

Trees in panels A, B & C were chosen for trial purpose in Perumcode area and it is as

following:

A panel – 45 trees – with cloth

B panel – 59 Trees – with cloth

B panel - 45 Trees – without cloth

C panel - 60 Trees – with cloth

Control - 10 Trees in each panel

The EM extended was prepared and applied on the following days

A Panel 6th

January

B Panel 6th

January

B panel 12th

January(without cloth)

C Panel 19th

January

The application of EMactivated was carried out daily (excluding holidays).The cloth was

washed and changed on 14th

April. The torn ones were replaced with new ones.

All operations were recorded and kept.

OBSERVATION

Preparation of the solution, care for the trees and application process are as expected. Cloths

tied around few trees were removed and observations were made for the incidence of the

dryness. The bark in general of the treated trees was wet compared to the trees which were

not treated. We could see speculations of latex on the tapping cuts in these trees whereas the

other trees were totally dry.

On seeing the wetness of the panel and drops of latex on the tapping cut there is hope of the

tree recovering from the dryness. Cankers are seen in older trees and in young trees

affected by the dryness. From the observation made planters deduce that the latex vessels

get thickened preventing further flow of latex (like veins / arteries getting thickened in

human body) leading to formation of cankers. The cankers arrest further flow of latex

through the vessels. Thus the dryness starts. Dr. Margarita Correa opines that the thickening

is due to the microbes( virus). As resistance of individual trees to these microbes vary some

trees are affected by the dryness (brownbast) when some or not. The EM act on the virus and

control the disorder. Also they impart resistance from further attack.

The response of the trees till May, 2004 so for is encouraging and we an anticipate

notable observation after a year only.

Start brown bast on the root The tree become unproductive

The trees affected are totally dry and then die

Brown bast in rubber tree

EMtreatment with cloth After 4 months treatment

Removing the clothes

Healing the rubber trees

Is there any latex after treatment?

Expectation and hope

Yes, there is !!!

Tree alive and productive again

Latex production Like normal rubber tree

Plot treated with EMand mulch system

Tree with more than 30 years old and canker Alive with latex again

Treatment in old trees Removing the clothes in the big trees

Looks healthy in the first glance

White fungus under the old treated skin

The new soft skin is complete healthy

Brown Bast as mentioned in Rubber Board Hand book

" Despite many approaches that have been made into the cause and effect of 'brown bast' there is a

long way to go before the complex sequence of events that culminate in the syndrome is understood.

Various histological investigations have been carried out on the bark of the brown bast affected trees

(31). Early investigators have related this phenomenon to the tree’s reaction to wound healing (31,34).

Brown bast is essentially a disorder of the latex vessels and the symptoms do not spread from virgin

bark to regenerated bark or from one regenerated panel to another, indicating that continuity of the

laticiferous vessel is necessary for its spread (29). It has been observed that it is possible to limit the

area of bark where the brown bast develops by isolating tapping panels with grooves on the bark up to

tapping depth. The affected portion of the bark stops yielding latex.

Various forms of physiological disorders commonly considered as brown bast were grouped into five

classes (7).

1.. Abnormal colour of the cut, brown spots and cracks in the bark with eventual necrosis and

stoppage of flow.

2.. Partial dryness without brown colour or necrosis.

3.. Woody burr formation resulting in deformation of the panel

4.. Coagulation of latex on the tapping cut with no flow of latex.

5.. Total dryness without brown colour or necrosis.

Usually, the actual onset of brown bast is preceded by an excessive dilution of the latex with late

dripping.

Whether this is a general rule for all the above classes of brown bast is doubtful. It has been noticed

that certain trees go dry with no earlier late dripping. It is possible that certain contradictory results

obtained by different workers may be due to the fact that they might have been dealing with different

types of brown bast.

Probably, owing to the practical difficulties in studying the progressive stages of brown bast, most of

the investigators have preferred by confine their study to the effect of brown bast. Schweizer (40)

associated

Brown bast with lack of organic reserves, while Beaufils (2) considered mineral metabolism to be the

causative factor. In support of his view, Schweizer induced conditions similar to brown bast by ring

barking above the tapping cut followed by intensive tapping. This cannot be considered as direct

evidence as the physiological exhaustion and the abnormal metabolism forced upon the tree with such

treatments need not be the same as that which predisposes the tree to brown bast under normal

conditions. Besides this, the results of later work stand against this contention as no evidence of starch

depletion in the bark or lowered sugar content in latex during the onset of dryness could be obtained

(5). The dry bark contained almost the same amount of total soluble sugars as that in the normal bark.

Efforts to correlate mineral content with brown bast incidence have not so far yielded any convincing

results. However, a significant inverse correlation was obtained between the K2O/Cao ratio in leaves

and the percentage of brown bast (coagulation at the tapping cut) (2). Incidence of such conditions

could be reduced by potash fertilizers. A higher Mg/P ratio was also recorded in latex in the

susceptible clones (AVROS 308 and GI 1) compared with resistant clones (PR 107). It is assumed that

the above mentioned disorder (coagulation at the tapping cut) is an extreme case of latex instability

and that Mg content of latex could be a determining factor. It has also been observed that conditions

similar to brown bast, induced by surgical treatments, resulted in very low flow rate of dilute latex

containing damaged bottom fraction particles and it is suggested that such extreme rate of flocculation

deep in the latex vessels may impede the flow, eventually inducing dryness (5). Role of divalent

cation in promoting the destabilising effect of lutoids is also known (33). In the majority of cases of

brown bast, however, a low dry of latex with late dripping, precedes the onset of dryness. Dilution of

latex can cause osmotic shock to the lutoid particles causing it to swell and burst. But the mechanism

by which a reduction in the rubber content is caused is far from clear. None of the above factors

reported can be considered responsible for it.

It is reported that by drastic tapping, the phospholipids and potassium increase with a simultaneous

reduction in the protein and calcium contents (40). A marked positive correlation between the stability

of latex and potassium content has been obtained (30). A high content of potassium in the latex of

brown bast affected trees is also reported. On the other hand, a high magnesium content of latex is

reported to be associated with precoagulation tendency of latex at the tapping cut (2). So, theoretically

it can be speculated that the reported brown bast conditions with high magnesium content and

coagulation at the tapping cut may well be distinct from the conditions of brown bast reported to be

associated with a high potassium content. Some clonal variations in the nature of brown bast

symptoms are also reported (7). On the other hand, other reports do not indicate any relationship

between brown bast incidence and soil type or soil and tree nutrient status (32).

The observations (7,52) that incidence of brown bast is greater during and after wintering deserve

further investigation. Fluctuation in the water relations as a consequence of excessive removal of latex

has also been suggested to be the causative factor (46). An abnormally strong dilution reaction during

latex flow was considered to favour the development of brown bast (15). In intensively tapped trees

initial flow rate and turgor pressure are found to be reduced before the onset of dryness (44). A view

has been expressed that wound reaction might lead to a reduction in the permeability of the wall of the

latex vessel resulting in a reduced availability of assimilates (1). In the same work a progressive

decline in the cation concentration of latices of the trees subjected to intensive tapping to induce

brown bast have been reported. Conversely, a higher concentration of cations in latices of intensively

tapped trees was reported in a later study and it has been suggested that changes in the cation

concentration might play a role in the observed deterioration of lutoids (29). With the aid of electron

microscope, evidence was provided for the flocculation of rubber particles around lutoid particles in

such latices and a hypothesis was proposed that coagulation of rubber particles inside latex vessels

due to decreased lutoid stability might be the causative factor for the onset of brown bast syndrome. It

was assumed that the histological characteristics of brown bast affected bark, such as tyloses and

stone cells, follow the development of disorders caused by damaged lutoids while features such as

tissue necrosis and hyperplasia of the surrounding cells follow the death of the vessels. In these

studies, phloem necrosis could not be detected and hence the earlier concept (6,20) that phloem

necrosis or senescence could be the primary cause of this disorder was ruled out.

The usual recommendation of giving tapping rest for six months for brown bast affected trees does

not always improve the situation. Usually, latex is found coagulated inside the vessels and giving rest

to the trees does not remove this condition. It is, therefore, recommended to remove all the diseased

tissues followed by continuous tapping off the remaining bark. If, however, the severity of the

disorder is such that the whole panel has been affected, upward tapping of such trees can be

considered.

The spectrum of views on the physiology of brown bast leaves behind the vital question how only a

few trees in a plantation of monoclonal budded material develop the brown bast symptoms. Much

more work is needed to elucidate the different stages of physiological disorders which culminate in

the brown bast syndrome."

Notes compiled and reviewed by Dr. Margarita Correa. May 2004